The present invention relates to a card which incorporates a semiconductor integrated circuit (hereinafter referred to as xe2x80x9cICxe2x80x9d) and more particularly to an IC card permitting either a contact coupling wherein signals are transmitted and received under the supply of electric power through a contact or a non-contact coupling wherein signals are transmitted and received under the supply of electric power through an antenna, with respect to an external device.
As known well, a contact type IC card is coupled to through a contact point to an external device, e.g., a data reader/writer (simply xe2x80x9creader/writerxe2x80x9d hereinafter), and performs the transmission and reception of signals between it and the reader/writer while being supplied with electric power through the contact point. On the other hand, a non-contact IC card is coupled to the reader/writer in a non-contact state through an antenna and performs the transmission and reception of signals between it and the reader/writer while being supplied with electric power through the antenna.
Recently, a single card which can operated in either the above contact or non-contact states has been devised or being developed as a dual interface IC card (see, for example, Published Japanese Translations of PCT International Publication for Patent Applications No. Hei 10-505932). The dual interface IC card is convenient for users and therefore its application range is being widened.
FIG. 4 shows the configuration of an internal circuit 12 in a conventional dual interface IC card. The internal circuit 12 is integrated into an IC chip. In case of operation in a non-contact state, electric power and signals are supplied through a coiled antenna 1, while in case of operation in a contact coupling state, electric power and signals are supplied through a contact point 2. As bidirectional signals to and from an information processor 3, signals having gone through either the antenna 1 or the contact point 2 are selected by a selector 4. For example, in the prior art being considered, the selection is made by detecting that electric power has been fed to a terminal Vdd of the contact point 2, which detection is performed by a voltage detector 11. As a result of the detection, the signals having gone through the contact point 2 are selected.
Usually, the information processor 3 has a processing unit and a memory and reads the contents of the memory in accordance with directions given by a reader/writer and provides a transmission signal or rewrites the memory contents in accordance with a reception signal provided from the reader/writer.
In a non-contact operation, electric power is obtained by rectifying a high frequency signal received by the antenna 1 in a rectifier 5, smoothing the rectified signal in a capacitor C and making the voltage thereof into a predetermined voltage in a series regulator 6. On the other hand, electric power from the contact point 2 is obtained directly from the reader/writer through the terminal Vdd.
Electric power and signals provided from the contact point 2 are defined by ISO7816 which is the international standard for contact type IC cards. Two kinds of supply voltages Vdd are defined therein, which are 4.5V-5.5V and 2.7V-3.3V. Further, it is defined therein that a minimum value at a higher signal level (xe2x80x9cHxe2x80x9d level) should be 0.7 Vdd. The internal circuit 12 in an IC chip constituted by the information processor 3, etc. is designed to operate with this voltage.
On the other hand, electric power and signals provided from the antenna 1 are supplied in a non-contact state from a reader/writer and the electric power to be supplied is limited. For this reason the circuit is required to operate at as low a voltage and power consumption as possible. In the case of an IC card used exclusively for a non-contact operation, a circuit is being developed which operates at a supply voltage of 2V or so.
However, the internal circuit 12 in the conventional dual interface IC card has been designed to operate at a low voltage in case of a non-contact operation and operate at a higher voltage, for example, 5.5V in case of a contact operation. Thus, although the internal circuit 12 can operate at a low voltage, a lowering of power consumption is obstructed and circuit components have so far been required to have a high voltage proof so as to withstand voltages provided from terminals of the contact point 2. An IC using transistors of a high voltage proof requires a complicated manufacturing step and thus an increase of cost is unavoidable.
It is an object of the present invention to provide an IC card low in both power consumption and manufacturing cost.
For achieving the above-mentioned object, the IC card of the present invention is characterized in that operating conditions in case of going through a contact point, which conditions are associated with supply voltage and signal level in an internal circuit, lie within operating conditions in case of going through an antenna.
Therefore, it becomes possible for the internal circuit to operate at low supply voltage and signal level common to both going through the antenna and going through the contact point. Thus, the power consumption is decreased. Besides, it becomes possible to set the voltage proof of circuit components at such a low level as has been adopted in the non-contact type. Consequently, it is possible to obtain an IC card easy to manufacture and low in cost.
The above operating conditions can be established by providing the IC chip with a voltage conversion means which converts the supply voltage provided through the contact point into a low voltage and a level conversion means which converts the signal level at the contact point into a signal level set in the internal circuit so as to decrease the signal level from the contact point and increase the signal level to the contact point.
Further, by providing the internal circuit with a voltage limiter means and by setting an output voltage of the voltage conversion means lower than a limit voltage set in the voltage limiter means, there can be obtained good results.